Was wondering if anyone has ever heard of this happening; the other day I was driving my S-Type and the timing chain slipped because the timing guides broke (this is not the odd part). Of course this has caused some issues, one of which is that somehow the piston head has hit one of the spark plugs (at least that is what the shop is telling me). I had the car towed to my house and will begin the process of tearing the heads off the block. My question is has anyone ever heard of this happening? It just seems strange that the piston would hit the plug, especially since the plug is ever present in the chamber.

 

Unfortunately, the timing guides do crack and eventually break. The same can be said of the tensioners. This is not odd. I think what your mechanic means is that the piston hit one (or more) of the valves. The 4.0 engine is an "interference" engine meaning once the timing is off - bad things will happen and rotating parts will make contact.

Once you start diving into this engine (good luck) if the above did happen - you are more than likely going to find more damage. The engine is more than likely not salvagable.

 

abonano may be correct regarding the 4.0 being an interference engine, I thought not, but he may be correct.

 

It might be that a broken off valve head has hit the plug, not actually the piston hitting the plug.

 

With regard to the Timing Chain Tensioner, I believe you can fit the modified Tensioner used on the 4.2 V8 which is of a more robust design and overcomes the problem you have experienced. Hopefully with the heads removed you may only find that you have to replace the damage valves and the piston/pistons that came into contact with the valve gear.
Will keep fingers crossed that the engine can be repaired.
If repairing ensure you rebuild the engine using the modified Tensioner.
Regards,
Inver.

 

To clarify - bfsgross is correct - this is a non-interference engine - my bad!

But, nonetheless when the guides or tensioners go more than likely you will find piston/valve damage.

The only way to clarify is to get into the engine and see what is damaged...

 

okay a broken valve hitting the spark plug makes sense, did not think of that. I am going to start breaking it down this weekend..... did I understand that a 4.2's timing setup (tensioner and guide) will work on the 4.0?

 

I believe this to be correct but will make sure of the facts and confirm. It may be that there is a modification that applies only to 4Ltr unit.
Regards
Inver.

 

Hi Mike
Just to correct my information re Timing Chain Tensioners.
There is an upgraded Tensioner for the 4Ltr V8 where they use an all metal unit (Mk3) instead of Plastic material used in the first 2 versions of the tensioners.
The 4.2 Ltr has double timing chains, so is a bit different, so please disregard my remarks referring to it.
The modification I had in mind is only for the 4Ltr unit and if you read the following information it will give you the full picture. http://www.jagservice.net/jaguar_V8_...tensioners.htm
Hope this is of assistance to you and sorry for any confusion I may have caused.
Regards,
Inver.

 

thanks for the information, I think that updating the tensioners will be better in the long run. would it have been possible that if something did come loose in the engine cylinder it would have broken the piston? My mechanic seems to think it may have but did not put a boroscope in the cylinder to see, he just said replace the motor.

 

Hi again,
Think it would be worth taking off the Cylinder Heads to see the extent of the damage. To put thing right it may just need some new valves in the Head. The company who supplied the information seem to think that this type of failure is repairable and rarely results in an engine Write-Off.
Lets hope they are correct and all goes well.
Regards
Inver.

 

So here is an update on the S-type, if you all are interested; took off the heads, the number 3 cylinder on the right bank pushed the valve head over into the spark-plug. It looks as though there is no damage to the piston head, so this is a good thing...... however I am not yet sure the damage to the head itself. the left side is perfect, so only one side at this point.

 

Hi,
Thanks for the update and hopefully the head will be okay to use again.
Keep us informed of the progress and hope you will soon have your S back on the road again.
Regards,
Inver.